Surface piercing drive technology and propeller tunnels are an established art which the inventor helped pioneer having been awarded U.S. Pat. No. 4,689,026, the contents of which are incorporated herein by reference. The drive systems can be highlighted by their ability to provide enhanced boat performance by use of the surface piercing propellers while safely placing such propellers beneath the hull of the water craft.
The obvious disadvantages of the surface piercing propellers may be found in reference to U.S. Pat. No. 5,667,415 issued to Arneson. The surfacing propeller is well known for its speed, as well as its lack of thrust at low speed, overloading its power source at preplane speeds and low thrust in reverse. Arneson has successfully commercialized surface piercing propellers which position a propeller near the surface of the water at a location outward from the transom of a boat. Air is drawn into and through the propellers and through the principles of compression/cavitation the propeller is able to function according to its design characteristics, thus leading to enhanced speed and performance derived from the surface piercing technology. Disadvantages to the surface piercing technology are mainly directed to the location of the propeller which is typically at the back of the boat. This interferes with the use of the back of the boat for fishing, diving or swimming and exposes the propeller to a position that is most dangerous. Representative disclosures relating to surface piercing technology can be found in U.S. Pat. Nos. 4,645,463 and 4,909,175.
Other disadvantages are the need to rotate the drives since they operate as a rudder and the inability to operate such drive systems at low speed which became the subject of the Arneson U.S. Pat. No. 5,667,415 previously mentioned. In this registration the invention discloses the use of a shroud that is placed around the propeller which prevents "walking" of the propeller at low speed but also protects individuals or marine life from impacting the propellers.
The directing of air to the propeller while it is beneath the boat provides a known benefit and is the subject of various types of prior art such as the following: U.S. Pat. Nos. 2,434,700; 3,702,485; U.S. Pat. No. Re. 23,105; U.S. Pat. No. Re. 38,522; U.S. Pat. Nos. 130,391; 807,769; 815,270; 1,081,876, 1,117,357; 1,262,942; 1,401,963; 2,138,831; 3,450,090; 4,031,846; 4,363,630; 4,383,828; 22,080; 965,870, 1,916,597; 1,966,029; 3,793,980; 3,937,173; 4,300,889; 4,443,202; 5,141,456; 5,405,278; 5,171,175; 5,667,415; 5,679,037; 4,977,845; 4,371,350; 4,993,349; 5,482,482; 5,588,886; and 4,941,423.
What is lacking in the art is the teaching of a surface drive technology that forms air passageways that enhance surface piercing propeller operation at all speeds and conditions and that particularly provides for a linearization of the relationship between vessel velocity and engine speed.